Reduced speed compensator for microwave heating applicator

ABSTRACT

A control circuit is disclosed for apparatus utilized in processing with microwave energy, such articles as pneumatic type rubber tires having nonuniform shaped bodies for pre-heating prior to vulcanizing or recapping. The articles to be heated are rotatably and axially moved within a microwave heating applicator and the energy is radiated by means such as horn antennas. Any loss of power in the microwave energy transmitter is automatically compensated for by reducing the programmed speed of movement by a factor commensurate with the loss of power to equalize the heating profile. Hence, if one of two 25KW transmitters were to fail, the speed of movement of the article being heated would be reduced by one-half. Means are also provided, such as an alarm, to alert the operator of the equipment failure.

United States Patent Peterson Dec. 16, 1975 [5 REDUCED SPEED COMPENSATOR FOR 3,614 366 10/1971 Huchok 2l9/l0.69 MICROWAVE HEATING APPLICATOR 13999189" g Ci Ct 21 [75] Inventor: Robert A. Peterson, Canton, Mass. ers n [73] Assignee: Raytheon Company, Lexington, Primary Examine" Bruce Reynolds Mass Attorney, Agent, or Firm-Edgar O. Rost; Joseph D Filed June 19 1974 Pannone; Harold A. Murphy 1211 Appl. No.: 480,657 1 1 AB TRACT Related U S Ap cation Data A control circuit is disclosed for apparatus utilized in C I t f 374 8 7 processing with microwave energy, such articles as 5" 0 1 June 1973 pneumat1c type rubber tires having nonuniform a an one shaped bodies for pre-heating prior to vulcanizing or recapping. The articles to be heated are rotatably and 8; "219/1055 g g g axially moved within a microwave heating applicator Fieid i. B 10 55 R and the energy is radiated by means such as horn an- A 55 M tennas. Any loss of power in the microwave energy 5 2 l transmitter is automatically compensated for by re- [56] Refe en e Ct d ducing the programmed speed of movement by a facr c s tor commensurate with the loss of power to equalize UNITED STATES PATENTS the heating profile. Hence, if one of two KW trans- 2,637,091 3/1953 Hagopian 219/1069 mitters were to fail, the speed of movement of the arti- 3,l82,166 5/1965 Bohm et a1 219/1055 M cle being heated would be reduced by one-half. Means are also provided, such as an alarm, to alert the opera- 1 ton f 3,541,289 11/1970 Smith 219/1055 A tor O the equlpment fallure- 3,584,389 6/1971 11111011 et al. 219/1055 A 4 Claims, 3 Drawing Figures TRANSMITTER TRANSMITTER /48 /50 /54 ROPO T SPEED SCAN AVXlAL D U COMPENSATOR SPEED SCAN DETECTOR CONTROL DRIVE TRANSMITTER SIGNAL 8 ALARM US. Patent Dec. 16, 1975 Sheet 1 of2 3,927,291

TRANSMITTER 4a 50 TRANSMITTER 8 AN XIAL DROPOUT SPEED SPCEED ScAN COMP AT DETECTOR ENS OR CONTROL DRIVE TRANSMITTER SIGNAL ALARM B /44 /52 H5 H5 VAC VAC TRANS A AXIAL SCAN DRIVE II5VAC BELL 52 TOGGLE SWITCH US. Patent Dec. 16, 1975 Sheet2 0f2 Illllllll'lllnlll...

REDUCED SPEED COMPENSATOR FOR MICROWAVEHEATING APPLICATOR- CROSS-REFERENCE TO REIJATED CASES BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relatesto an electrical control circuit for microwave heating applicators wherein articles of large mass are moved continuously during processing to establish a predetermined heating profile.

2. Description of the Prior Art In the rubber industry vulcanizing and molding, as well as, recapping of pneumatic type tires has been time consuming due to the inherent poor thermal conductivity of rubber material. Such articles are generally heated from the outside and in many instances it may take hours to reach the required working temperature. The materials used in the applicable articles incorporate both natural as well as synthetic rubber along with other ingredients including carbon-derived products. The compounded material has an inherent ability for being treated with electromagnetic energy to thereby provide for more rapid generation of heat by absorption. Carbon-derived products, such as carbon black,

' are ideal electromagnetic energy absorbing materials to aid in.the microwave heating process.

Microwave heating applicators are now widely utiliz ed in the processing of nonconductive or poor thermally ;conductive materials such as foods, paper, wood,

leather, plastics and the like. The high frequency enare 915 i 13MHZ and 2450 i SOMHZ or the so-called industrial scientific medical band. In the present application the term microwave is defined as electromagnetic energy radiation having wavelengths in the order of 1 meter to l millimeter and frequencies in the order of 300 MHz to 300 GHz.

An example of prior art microwave heating applicators for preheating rubber tires is disclosed in US. Pat. No. 3,566,066, issued Feb. 23, 1971, to J. Borthwick and E. Searle. In this reference a chamber of a substantially circular, elliptical or smooth curved cross-sectional configuration is provided with an assymmetrically located waveguide feed disposed in the base. Multimode distribution means comprising a motor driven vane-type mode stirrer is disposed adjacent to the waveguide feeding means. A rotatable disc within the chamber carries the article to be heated and is energized by a shaft and motor.

Another example of the prior art teachings is found in copendingapplication Ser. No. 227,547, filed Feb. 18, 1972, by R. A. Peterson and C. L. Gilliatt, and assigned to the assignee of the present invention. This apparatus provides for processing very large diameter pneumatic type rubber tires with a heating applicator including an enclosure having. at least one flared horn antenna radiator heating specific areas of the tire. The ends of the radiator surrounding the open mouth are 2 shaped to have a contour substantially conforming to that of the article being processed and path of travel. A supporting structure is positioned within the heating applicator and such support means are vertically, as well as rotatably, displaced by suitable gearing means to provide for the uniform application of the microwave energy across the entire surface of the article being processed. Since the articles being heated have substantially nonuniform cross-sectional areas with the thicker region in the central area of the tread varying heating times are required to substantially equalize the overall temperature of the article prior to subsequent processing operations which may be either vulcanizing or recapping. Tires having a diameter of up to 15 feet are easily accommodated by the enclosure having movable sidewalls. To heat such articles the microwave power is of such a substantial nature and numerous transmitters are required to operate numerous individual microwave energy sources. As the article to be heated is continuously rotated and moved axially past the energy radiating means the speed of movement is programmed to obtain the desired temperature profile across the entire article. Hence, in the areas of thicker or the tread sections much higher heat concentration is required while lower heat is required for the sidewalls. In the overall processing of articles by microwave energy involving rotation as well as axial displacement and a rather large mass required to be heated, the failure of one or all of the power sources could result in considerable damage to the product by failure to achieve the desired temperature profile. This could be quite costly in view of the great expense of the articles such as the giant tires which may cost many thousands of dollars. A need arises therefore, for rapid and automatic control of the programmed movement of an article being heated with. microwave energy or the complete shutdown of the apparatus to compensate for diminution of power due'to source failures.

SUMMARY OF THE INVENTION In accordance with the present invention an electrical control circuit is disclosed for microwave heating applicators having rotatable and axially displaceable product-carrying means to automatically compensate for any loss of power from-the energy source means by reducing the speed of movement of the product-carrying means by a factor commensurate with overall loss of power. The temperature profile across the article, such as a pneumatic type rubber tire, having a nonuniform cross-sectional area is thereby temporarily adjusted to provide for substantially uniform heating until full power is restored. Additionally, means are disclosed to alert the operator at the time of the equipment failure in order that suitable repairs may be instituted.

BRIEF DESCRIPTION OF THE DRAWINGS Details of the illustrative embodiment of the invention will now be described with reference being directed to the accompanying drawings, wherein:

FIG. 1 is a diagrammatic representation of the embodiment of the invention;

FIG. 2 is a schematic circuit diagram of the illustrative embodiment of the invention; and

FIG. 3 is a detailed plan view of a microwave heating applicator embodying the invention with the top wall partially displaced to disclose internal structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 3 will be described. In this embodiment a large sized rubber tire is mounted on turntable 12 which is adapted to both rotate and vertically displaced at a programmed rate of movement by such structure as that disclosed in the referenced pending patent application which provides for the rotation of the tire at speed illustratively 4 rpm. While the tire casing is rotated, vertical displacement of the article will provide for heating to temperatures at approximately 200F in the center sections of the tire while the sidewalls remain at approximately 100F or below. Numerous differential gear structures are disclosed in the referenced pending application and need not be further elaborated on for the purpose of describing the present invention.

The microwave heating applicator comprises a plurality of high voltage power supplies 14 shown with doors 16 open and are of the conventional power supplies employed for electromagnetic energy generators of the magnetron type. The high power electromagnetic energy is coupled by means of rectangular waveguides 18 including energy sealing bellows arrangements 20 secured to movable walls 22. Electrical power cables 24 and coolant circulation conduit means 26 are coupled to each of the power supplies.

. Plural horn antenna radiator means 28 are contoured at the open ends 30 to substantially conform to the shape of the article being processed. The radiator means 28 being carried on the inside of the movable walls 22 can be disposed at any desired position as indicated by the dashed lines. The movable walls are carried along with the high voltage power supplies by means of wheels 23. Parallel sidewalls 32 are fixed and provided with access means such as a door. The top wall of the overall microwave heating applicator is formed by sliding sections '34 supported by wheels 36 which are actuated by gears 38 and chains 40. In the view shown the left-hand portion illustrates the sliding wall section in the open position and has been designated 34a. The right-hand portion of the view indicates the closed position of the top wall section 34. In normal operating conditions the sliding wall sections open and close simultaneously and a crane or other suitable elevating means is utilized to position the article to be heated on the turntable 12. The dashed lines in FIG. 3 indicate the movable positions of the described components as well as underlying structures.

In accordance with the invention means are provided for compensating for any power failure in the overall high voltage transmitters or the energy sources. In the disclosed embodiment four such transmitters have been shown and while only oppositely disposed radiator means 28 are shown it is possible, in accordance with the teachings of the referenced copending application, to provide four such radiators to radiate all quadrants of the rotating article being heated. It is also permissible to provide for a staggering of the individual radiators at different levels to all selectively heat different regions of the rotating article.

Referring next to FIGS. 1 and 2 the electrical circuit for reflecting changes in the power levels of the energy being radiated within the enclosure will now be described. The illustrative circuit provides for reduced with transmitters 42, 44 including the high voltage supplies and energy sources which are interconnected by a drop-out detector circuit 46. If one of the transmitters should fail during the heating process, the article being heated would then be subjected to less power during the remainder of the cycle since the axial speed of the article is programmed to obtain the desired temperature profile across the overall cross section. A signal from the drop-out detector causes a resistance voltage divider compensator circuit, to be described in greater detail in reference to FIG. 2 designated by the block 48, to be energized in the motor speed control circuit which reduces the speed of the scan control 50. Simultaneously, the signal from the drop-out detector alerts the operator for the condition by means of the actuation of any suitable signal alarm 52. The scan speed control 50 regulates the movement of the article being heated so that the speed is cut back in appropriate proportion commensurate with the amount of the power loss. If one of two transmitters should fail, the speed is reduced to one-half; if one of five transmitters fail, the speed would be four-fifths of normal; etc. Should all the transmitters fail to result in a total loss of power, the entire process would stop until at least one of the transmitters is turned on.

In FIG. 2 an exemplary schematic of a speed compensator electrical circuit 48 is disclosed. A set of relays designated RY l-4 inclusive is shown to reduce the motor control speed by a factor determined by the overall loss of heating power. Terminal board 56 provides for the interconnection of the electrical components of the overall circuit. Each relay is shown with the solenoid coil designated by a circle, the contacts by the parallel disposed lines and the resistor which is cut into the circuit at the appropriate time by the standard resistor electrical designation. Hence coil 58, contacts 59 and 60 and resistor 61 comprise the first relay designated RY-l. Similarly, relay RY-2 comprises coil 62, contacts 63 and 64 as well as resistor 65. The alarm means 52 are also energized by the relay RY-2. Another relay RY-3 includes coil 66 and contacts 67 and 68 interconnected to the alarm system 52. Finally, relay RY-4 includes coil 69 and contacts 70. Toggle switch contacts 71 and 72 provide for the energizing of the control circuit.

A source of voltage, illustratively, IISVAC, for transmitter 42 appears across terminals 1 and 9 when it is operative and the similar voltage value from transmitter 44 across terminals 2 and 8. When transmitter 44 is on RY-2 is energized and when transmitter 42 is on RY-4 is energized. Relays RY-l and RY-3 are energized when both transmitters are on. The toggle switch provides for on or off control of the Automatic Circuit means. Resistors R and R261 provide a voltage divider circuit which is connected between the speed control 50, potentiometer R3 and the axial scan drive control 54. When switch contacts 71 are closed, series resistor R165 is shorted to open the circuit to shunt resistor R261 thereby eliminating the divider from the control circuit. A similar result occurs with relay RY-l being energized by contacts 60. This provides for a reduction of speed when a transmitter fails. The alarmsignal 52 is actuated when either relays RY-2 or RY-4 are energized and when relay RY-3 is not energized. Since RY-2 energizes only when transmitter 44 is on and relay RY-4 energizes when transmitter 42 is on, the

alarm bell will ring when only one transmitter is generating power. Relay RY-3 energizes when both transmitters are on closing contacts 67 and 68 therefore, the alarm circuit will only be energized when there is a failure to alert the operator.

There is thus disclosed means for automatically compensating for any loss in power in a microwave heating applicator, particularly, useful where articles of high cost and programmed temperature profiles are involved. Numerous modifications, variations and alterations will be evident to those skilled in the art. The foregoing description of the embodiment, therefore, is

intended to be interpreted broadly rather than in a limiting sense.

I claim:

1. Microwave heating apparatus comprising:

an enclosure;

plural interconnected sources of electromagnetic energy;

means for radiating said energy within said enclosure;

means for positioning an article to be heated within said enclosure;

said positioning means having a programmed rate of movement controlled by a speed control electrical positioning means comprise means for rotating said article during heating.

3. The apparatus according to claim 1 wherein said positioning means comprise means for rotating and axially displacing said article during heating.

4. The apparatus according to'claim l and alarm means energized by said drop-out detector circuit to alert the operator of the reduction of power condition of said apparatus. 

1. Microwave heating apparatus comprising: an enclosure; plural interconnected sources of electromagnetic energy; means for radiating said energy within said enclosure; means for positioning an article to be heated within said enclosure; said positioning means having a programmed rate of movement controlled by a speed control electrical circuit to heat said article to obtain a desired temperature profile; and electrical circuit means including a drop-out detector circuit to detect the failure of at least one of said sources to operate and generate an output signal and a speed compensator circuit energized by said output signal interconnected to said speed control circuit to reduce movement of said article positioning means by a factor commensurate with the reduction of power resulting from said source failure.
 2. The apparatus according to claim 1 wherein said positioning means comprise means for rotating said article during heating.
 3. The apparatus according to claim 1 wherein said positioning means comprise means for rotating and axially displacing said article during heating.
 4. The apparatus according to claim 1 and alarm means energized by said drop-out detector circuit to alert the operator of the reduction of power condition of said apparatus. 